Sliders bonded by a debondable encapsulant containing styrene and acrylate polymers

ABSTRACT

The invention relates generally to the bonding of one or more sliders in styrene and acrylate polymers. More particularly, the invention relates to planarized slider assemblies formed by using debondable solid encapsulants comprised of styrene and acrylate polymers. The invention also relates to methods that use such encapsulants in conjunction with resists to produce magnetic head sliders having patterned air-bearing surfaces.

TECHNICAL FIELD

The invention relates generally to the bonding of one or more sliders instyrene and acrylate polymers. More particularly, the invention relatesto planarized slider assemblies formed by using debondable solidencapsulants comprised of styrene and acrylate polymers. The inventionalso relates to methods that use such encapsulants in conjunction withresists to produce magnetic head sliders having patterned air-bearingsurfaces.

BACKGROUND

A magnetic storage system typically includes one or more magneticrecording disks having surfaces from which data may be read and to whichdata may be written by a read/write transducer or “head.” The transduceris supported by an air-bearing slider that has a top surface attached toan actuator assembly via a suspension, and a bottom surface having anair-bearing design of a desired configuration to provide favorableflying height characteristics. As a disk begins to rotate, air entersthe leading edge of the slider and flows in the direction of thetrailing edge of the slider. The flow of air generates a positivepressure on the air-bearing surface of the slider to lift the sliderabove the recording surface. As the spindle motor reaches the operatingRPM, the slider is maintained at a nominal flying height over therecording surface by a cushion of air. Then, as the spindle motor spinsdown, the flying height of the slider drops.

The manner in which a slider is manufactured can affect flying height.Preferably, variations in the physical characteristics of the slider,e.g., those due to manufacturing tolerances, should not substantiallyalter the flying height of the slider. If this result is not achieved,the slider's nominal flying height must be increased to compensate forvariations between sliders.

A number of technologies may be employed to pattern such slidersurfaces. For example, mechanical processes such as cutting or abrading,have been proposed to remove material from a slider surface. Similarly,non-mechanical processes such as laser ablation, in which high intensitylight is used to evaporate material from sliders, have also beenproposed. Alternatively, material may be added to slider surfaces toalter their configuration to provide favorable flying heightcharacteristics. In some instances, these technologies have been used inconjunction with photolithographic and other semiconductor processingtechniques. In addition, these technologies may be adapted to pattern aplurality of air-bearing slider surfaces simultaneously and/orsystematically.

Thus, a number of approaches have been developed to facilitate thehandling of a plurality of sliders for simultaneous and/or systematicpatterning of their air-bearing surfaces. For example, U.S. Pat. No.5,932,113 to Kurdi et al. describes a method for preparing theair-bearing surface of a slider for etch patterning. The method involvesapplying first and second thin films comprising, respectively, first andsecond air-bearing surfaces, to a carrier in a manner such that thefirst and second thin film are separated by a recess. An adhesive filmis applied over the first and second thin films adjacent to the firstand second air-bearing surfaces. Then, a curable acrylate adhesive fluidis deposited in the recess and held therein by the adhesive film. Oncethe fluid is cured, the adhesive film is removed. The resulting sliderassembly may then be patterned by etching. For example, the first andsecond air-bearing surfaces may be coated with an etch mask, which isthen developed to allow for the patterning of the first and secondair-bearing surfaces.

Similarly, U.S. patent application Ser. No. 6,106,736 to LeVan et al.describes a method of preparing an air-bearing surface of a slider foretch patterning. The method involves applying first and second sliders,each comprising an air-bearing surface, to a substrate, such that thesliders are separated by a recess and the air-bearing surfaces areexposed. The substrate is placed into a frame, and a contiguous adhesivefilm is applied across the substrate and frame and positioned adjacentto the air-bearing surfaces. Subsequently, a heated wax is deposited inthe recess and cooled, and the adhesive film is removed.

In short, these approaches employ an encapsulant to fill the gapsbetween sliders to protect the edges of the sliders during patterning.However, these encapsulants suffer from a number of disadvantages. Forexample, the curable encapsulants described in Kurdi et al. and thewaxes described in LeVan et al. often exhibit unfavorable bonding and/ordebonding performance. In particular, cured epoxy materials, e.g., purethermosetting epoxy resins, can be removed from sliders only with greatdifficulty and often leave significant material residue on the slidersurfaces. In addition, the prior art encapsulants suffer fromincompatibility with solvents that are used with the photothographictechniques for patterning air-bearing surfaces. That is, the prior artencapsulants are mechanically unstable and are subject to solvation whenexposed to fluids used in photolithographic techniques.

Thus, there is a need in the art to overcome the disadvantagesassociated with prior art encapsulants. This has been accomplished bythe instant invention, which provided for improved slider assemblies andmethods for patterning air-bearing surfaces of sliders using debondableencapsulants.

SUMMARY OF THE INVENTION

Accordingly, one aspect of the invention relates to a slider assemblyformed using a debondable solid encapsulant comprising styrene andacrylate polymers.

Another aspect of the invention pertains to a method for forming suchsliders assemblies.

Yet another aspect of the invention provides methods for using adebonable solid encapsulant comprising styrene and acrylate polymers topattern an air-bearing surface of a slider.

Additional aspects, advantages and novel features of the invention willbe set forth in part in the description that follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing, or may be learned by practice of the invention throughroutine experimentation.

In a first embodiment, the present invention provides a slider assemblycomprising a plurality of sliders bonded by a debondable solidencapsulant. The encapsulant is comprised of styrene and acrylatepolymers. Each slider has a surface that is free from the encapsulant,and the encapsulant-free surfaces are coplanar to each other.

Typically, the slider assembly has a contiguous planar surface comprisedof at least one encapsulant region and containing the coplanar slidersurfaces. In addition, the sliders may be arranged in an array, e.g.,rectilinear array, such that the sliders do not contact each other. Thecoplanar surfaces of the sliders may be air-bearing surfaces.

In another embodiment, the invention provides a method for forming aslider assembly. The method involves arrange a plurality of sliders eachhaving a surface such that the surfaces are coplanar to each other. Anencapsulant fluid comprising a styrene and acrylate moieties isdispensed in a manner effective to bond the sliders without contactingthe coplanar slider surfaces. Typically, the fluid is comprised of astyrene polymer and an acrylate composition. The dispensed encapsulantfluid is subjected to conditions effective for the fluid to form adebondable solid encapsulant comprising a styrene and acrylate polymers.

In some instances, other encapsulation fluids may be used as wellcomprising a first polymer and a composition that is polymerizableand/or crosslinkable in a manner effective to bond the sliders withoutcontacting the coplanar slider surfaces.

Typically, sliders are arranged on a laminate of a flexible tape and anadhesive such that slider surfaces contact the adhesive. In such a case,the adhesive is preferably resistant and optimally impervious tosolvation by the encapsulant fluid.

In a further embodiment, the invention provides a method for patterningan air-bearing surface of a slider. A resist layer is applied on anair-bearing surface of a slider such that at least a portion of theslider other than the air-bearing surface is encapsulated in adebondable solid encapsulant comprising styrene and acrylate polymers. Aportion of the resist layer is removed to uncover a portion of theair-bearing surface in a patternwise manner. Material may be added to,or more typically, removed from the uncovered portion of the air-bearingsurface. As a result, the air-bearing surface of the slider ispatterned. The encapsulant is mechanically stable upon exposure to anyfluid employed to effect patterning of the air-bearing surface.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates a prior art slider having roundedcorners and edges.

FIGS. 2A–2F, collectively referred to as FIG. 2, depict an example ofthe inventive slider assembly as well as a method for forming theassembly. FIGS. 2A and 2B depict the arrangement of sliders in arectilinear array on a substrate in the form of a tape having apressure-sensitive adhesive coated on an upper surface thereof in topview. FIG. 2B depicts the arrangement of sliders of FIG. 2A incross-sectional view along dotted line A. FIGS. 2C and 2D depict theformation of an encapsulated array in top and cross-sectional views,respectively. FIGS. 2E and 2F depict the encapsulated array of FIGS. 2Cand 2D attached to a carrier and having the tape removed in top andcross-sectional views, respectively.

FIGS. 3A–3E, collectively referred to as FIG. 3, depict an example of amethod for photolithographically patterning an air-bearing surface of aplurality of sliders provided in the form of the slider assemblydepicted in FIG. 2. FIG. 3A depicts in cross-sectional view theapplication of a photoresist layer on the air-bearing surface of theslider assembly. FIG. 3B depicts in cross-sectional view the patternwiseexposure of the photoresist layer. FIG. 3C depicts in cross-sectionalview the removal of the resist layer according to the pattern formed inFIG. 3B. FIG. 3D depicts in cross-sectional view the removal of materialfrom the exposed slider surfaces. FIG. 3E depicts in top view debondedsliders having patterned air-bearing surfaces.

DETAILED DESCRIPTION OF THE INVENTION

Definitions and Overview

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to processing conditions,manufacturing equipment, or the like, as such may vary. It is also to beunderstood that the terminology used herein is for describing particularembodiments only and is not intended to be limiting.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a resist layer” includes a single resist layer as well asa plurality of resist layers, reference to “a slider” includes a singleslider as well as a plurality of sliders, and the like.

In describing and claiming the present invention, the followingterminology is used in accordance with the definitions set out below.

The term “array” as used herein refers to a two-dimensional arrangementof items such as an arrangement of sliders. Arrays are generallycomprised of regular, ordered items as in, for example, a rectilineargrid, parallel stripes, spirals, and the like, but non-ordered arraysmay be advantageously used as well. In particular, the term “rectilineararray” as used herein refers to an array that has rows and columns ofitems wherein the rows and columns typically, but not necessarily,intersect each other at a ninety-degree angle. An array is distinguishedfrom the more general term “pattern” in that patterns do not necessarilycontain regular and ordered features.

The term “bond” is used herein in its ordinary sense and means to joinsecurely. Typically, but not necessarily, “bonding” is achieved throughadhesive forces. Similarly, the term “debondable” as in “debondableencapsulant” refers to an encapsulant that is susceptible to completeremoval from the surfaces of items bonded thereby without damage to theitems.

The term “encapsulant” refers to a material suited to bond a pluralityof items or to encase one or more items in a confined space. Typically,an “encapsulant” is a solid material formed from an “encapsulant fluid”that has been subjected to conditions effective for solidification tooccur.

The term “fluid” is generally used in its ordinary sense and refers tomatter that is capable of flow. Typically, but not necessarily, a fluidcontains a liquid and optionally a solid or a gas that is minimally,partially, or fully solvated, dispersed, or suspended in the liquid. Forexample, a fluid may be aqueous or nonaqueous in nature and may containorganic solvents and the like having polymers and/or monomers solvatedtherein.

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.

The term “polymer” is used herein in its conventional sense to refer toa compound having two or more monomer units, and is intended toencompass homopolymers as well as copolymers, including, for example,graft copolymers. The term encompasses polymers of all types and is notlimited to linear, branched, cyclic, or crosslinked polymers. Thus, forexample, a styrene polymer contains at least one monomeric unit having astyrene structure, an acrylate polymer contains at least one monomericunit having an acrylate structure, and a butadiene polymer contains atleast one monomeric unit having a butadiene structure.

The term “solid” is used in its ordinary sense and refers to items thathave definite shape and volume.

The term “substantially” as in, for example, the phrase “substantiallyindentical in geometric dimensions” refers to items having dimensionsthat that do not deviate from each other by more than about 10%.Preferably, the difference in the dimensions is no more than 1%.Optimally the difference is no more than 0.1%. Other uses of the term“substantially” involve an analogous definition.

Slider Assembly

Generally, the invention relates to the patterning of an air-bearingsurface of a slider. Accordingly, various embodiments of the inventionprovide slider assemblies that may be used in conjunction with suchsurface patterning processes. In order to elucidate the invention fully,a known slider is illustrated in FIG. 1. As with all figures referencedherein, in which like parts are referenced by like numerals, FIG. 1 isnot to scale, and certain dimensions may be exaggerated for clarity ofpresentation. A slider 100 having a generally rectangular air-bearingsurface is depicted in FIG. 1. Located on the air-bearing surface ofslider 100 are leading pads 101 and 102 disposed on a first shallow stepregion 110. Additionally, the slider 100 includes a trailing pad 103disposed on a second shallow step region 111. The shallow step regions110 and 111 are approximately the same depth with respect to theair-bearing surface.

The shallow step region 110 extends along the leading edge 140 of slider100 and has side rails that extend along the side edges 150 and 151 ofslider 100. The shallow step regions 110 and 111 provide the positivepressure regions of slider 100. More specifically, the shallow stepregion 110 pressurizes leading pads 101 and 102 and shallow step region111 pressurizes trailing pad 103 during operation, to give slider 100 apositive lift. Pressurization mainly occurs at the step transitionbetween the shallow step regions and the air-bearing pads. The negativepressure region 120 is responsible for pulling slider 100 towards thedisk surface during operation. During operation, the disk is rotatingand the slider is flying above the disk surface. In general, thenegative and positive pressure regions of slider 100 are counterbalancedto provide a relatively flat flying height profile.

It should be evident from the slider depicted in FIG. 1 that the stepson the air-bearing surface must be patterned with sufficient precisionto provide a desired flying height profile. Although the size of thesliders may vary, recent advances in slider processing technology allowfor the production of sliders having a rectangular air-bearing surfacearea on the order of 1 mm² or less. Accordingly, there is an increasingdemand for technologies that effect precise control over the placementand spatial orientation of slider surfaces when the surface ispatterned.

To this end, the invention provides a slider assembly comprising aplurality of sliders. The sliders are bonded by a debondable solidencapsulant. Depending on the processing techniques that may be used inconjunction with the assembly, certain bonding materials areparticularly suitable for use as encapsulants. Selection criteria forsuitable encapsulant are discussed below.

The invention may be employed using sliders composed of any materialsuitable for use as a slider having appropriate thermal, electrical,magnetic and mechanical properties. Typically, sliders for magneticheads are made from a hard material having a high modulus of elasticity.Such materials include ceramics such as carbides, nitrides, and oxides.Carbides such as aluminum carbide, silicon carbide, titanium carbide,boron carbide, geranium carbide, tungsten carbide, and mixed-metalcarbides (e.g., AlTiC or Al₂O₃TiC) are generally preferred but othermaterials such as titanium oxide, silicon nitride and silicon may beused as well. In addition, it is preferred that the slider is sized torequire only minimal material addition or removal in order to patternthe air-bearing surface.

Thus, sliders may be formed by first cutting a monolithic solid memberinto the plurality of sliders. The monolithic solid member may be grownor prepared in bulk, and depending on desired properties, the materialmay have a single crystalline, multicrystalline, or amorphousmicrostructure. Exemplary techniques for forming monolithic materialsinclude Czochralski, float zone and other methods known in the art.

Irrespective of the encapsulant employed to form the slider assembly,each slider of the assembly has a surface that is free from theencapsulant. These surfaces are coplanar to each other and typicallyrepresent air-bearing surfaces of the sliders. The coplanar arrangementof the slider surfaces is well suited for use in numeroussurface-patterning techniques such as those involving the use of maskingtechnology and/or the employment of photolithographic techniques. Insome instances, the slider assembly has a contiguous planar surfacecomprised of at least one encapsulant region and containing the coplanarslider surfaces. Such planar surface contiguity facilitates thedeposition of a uniform and/or contiguous film or coating on thecoplanar slider surfaces. In some instances, the slider has anadditional planar surface opposing the coplanar sliders surfaces. Theadditional planar surface may or may not be contiguous and may be formedfrom the encapsulant and/or a slider. Such an additional planar surfacemay further facilitate ease in the-handling of the assembly.

In certain embodiments, the sliders of the assembly are substantiallyidentical in geometric dimensions. In addition, the sliders aretypically arranged in an array such that the distance between thesliders is minimized without having the sliders contact each other.Contact among the sliders increases the likelihood of slider damage.Often, rectilinear arrays are chosen to maximize the slider toencapsulant volumetric ratio.

The inventive slider assembly may be used as a convenient means forhandling and processing a plurality of sliders. To ensure that thesliders remain immobilized with respect to each other, the encapsulantmay be rigid. In addition or in the alternative, the. slider assembly asdescribed above may further include a carrier attached to theencapsulant and/or at least one slider. The carrier is particularlyuseful when the encapsulant is brittle or otherwise difficult to handle.Usually, the carrier does not cover any of the coplanar slider surfaces.

The encapsulant may be selected for certain properties that willfacilitate its use in slider patterning techniques. While specificmaterials suitable for use as an encapsulant are discussed below,encapsulant materials generally share some common characteristics. As aninitial matter, the encapsulant should be able to bond with the slidersin a void-free manner without debonding until after patterning processeshave been completed. Because bonding behavior is often surfacedependent, the encapsulant should be selected according to the surfaceto which bonding is to take place. Particular attention should be paidto factors such as surface composition, morphology, and the like.

In addition, the encapsulant should be able to maintain its mechanicalstability until debonding is desired. Furthermore, the encapsulantshould be readily debonable without damage to the sliders and withoutleaving any residue on the sliders. For example, the encapsulant may bedebonded through washing in a solvent capable of solvating theencapsulant or a component thereof. In addition, or in the alterative,heat may be applied to liquefy, vaporize and/or discompose theencapsulant.

Thus, it should be evident that the encapsulant should be able towithstand the environmental conditions imposed on the sliders duringpatterning. For example, some slider patterning techniques require theexposure of sliders to a vacuum. Any outgassing from the encapsulant maycompromise the quality of the vacuum. Thus, it is sometimes preferredthat the encapsulant does not substantially outgas under vacuum. Asanother example, slider-patterning techniques may require thermalcycling of the sliders. Accordingly, it is preferred that theencapsulant be mechanically stable for thermal cycling e.g., from about20° C. to about 100° C.

Method for Forming a Slider Assembly

The invention also provides a method for forming a slider assembly. Themethod involves arranging a plurality of sliders each having a surfacesuch that the surfaces are coplanar to each other. An encapsulant fluidis dispensed in a manner effectively to bond the sliders withoutcontacting the coplanar slider surfaces. The dispensed encapsulant fluidis subjected to conditions effective for the fluid to form a debondablesolid encapsulant from the encapsulant fluid.

Due to the precision required for forming the slider assembly and thesize associated with the sliders, manual slider placement is typicallyundesirable. Instead, automated and/or robotic means for positioning orarrange the sliders may be preferred. Selection of an appropriate meansfor positioning or arranging the sliders depends on the speed andaccuracy required. In some instances, the sliders may be placedsimultaneously. In other instances, the sliders may be successivelyplaced. One of ordinary skill in the art will recognize that positioningmeans, may be constructed from, for example, motors, levers, pulleys,gears, a combination thereof, or other electromechanical or mechanicalmeans.

In order to maintain the sliders in proper position and spatialorientation to allow for solidification of the encapsulant to occur, ameans for immobilizing the sliders may be employed. For example, thesliders may be arranged on a substrate surface and immobilized thereonthrough mechanical action (e.g., clips, centripetal force),electrostatic attraction, magnetic forces, or other known immobilizingmeans. In some embodiments, the sliders may be temporarily immobilizedon a substrate through the application or use of an adhesive on thesubstrate surface, e.g., pressure sensitive adhesives such as acrylics,natural rubbers, butyl rubbers, polyvinylethers, silicones, and mixturesthereof. As the performance of pressure adhesives may vary withtemperature, an adhesive may be selected to exhibit improved performanceat temperatures ranging from about 25° C. to 30° C. The pressure ofapplication may range from about 10 lbs/cm² to 50 lbs/cm² and preferablyis about 25 lbs/cm². To deter the adhesive from leaving residue on theslider, the adhesive should preferentially adhere to the substrate overthe air-bearing surfaces.

As discussed above, the encapsulant fluid is dispensed in a mannereffective to bond the sliders without contacting the coplanar slidersurfaces. Thus, when the substrate surface is planar, the air-bearingsurfaces of the sliders may be placed in contact with the substratesurface to ensure that the air-bearing surfaces remain coplanar as wellas to deter contact with the encapsulant fluid. Any adhesive used shouldbe resistant or impervious to solvation by the encapsulant fluid or acomponent thereof to deter wicking of the encapsulant fluid via theadhesive to contact the slider surfaces.

The substrate may be comprised of any material compatible with theencapsulant fluid. In addition, the substrate is preferably selectedfrom a material that is softer than the slider to avoid damaging anyslider surface that comes into contact therewith. In some instances, aflexible substrate may be used to facilitate its removal. For example,any number of polymeric films may be used such as those derived frommonomers including ethylene, propylene, butylene and, homopolymers andcopolymers of these olefins; vinyl monomers such as vinyl acetate, vinylchloride, vinylidene chloride, vinyl fluoride, acrylonitrile, methylmethacrylate and mixtures thereof; of ethylene with portions of one ormore unsaturated monomers such as vinyl acetate, acrylic acid andacrylic esters; as well as styrenes, carbonates, esters and urethanes.Polymers capable of withstanding relatively high temperatures, such aspolyimide may be a desirable substrate material when the substrate maybe exposed to a high temperature. Polyimides are commercially available,e.g., under the tradename Kapton®, from DuPont (Wilmington, Del.).

Thus, it should be apparent that the substrate may be a laminate of aflexible tape and an adhesive, wherein the adhesive is in contact withthe air-bearing surfaces. Exemplary adhesive thicknesses may range fromabout 2 to about 25 micrometers and the tape thickness may range fromabout 12 to about 150 micrometers.

The adhesive strength of the adhesive film varies from about 50 gm/20 mmup to about 100 gm/20 mm. Commercially available adhesive films includeV-8-S from Nitto Denko, which is a polyvinyl chloride based tape havinga 10 micrometer thick adhesive layer, a 70 micrometer thick polyvinylchloride flexible substrate and 100 g/20 mm of adhesion. Another film isthe Nitto Denko V-8-T, having the same constitution as the V-8-S filmwith 50 gm/mm of adhesion.

Other useful films include Nitto Denko's BT-150E-EL film having 75 gm/20mm of adhesion, an ethylene vinyl acetate based tape having a 15micrometer thick adhesive layer; Lintec's Adwill P-1600 B film, which isa water flushable tape having a base material of polyolefin which is 110micrometers thick, an adhesive layer of polyacrylate which is 20micrometers thick and has adhesion of 140 gm/25 mm. In some instances,polyesters such as polyethylene terephthalate may be used as a tapematerial. For example, substrates comprised of a laminate of apolyethyelene terephthalate tape having a thickness of about 37micrometers and an adhesive layer of about 5 micrometers are availablefrom 3M Corporation (St. Paul, Minn.).

As discussed above, the sliders are typically arranged in a rectilineararray on a planar substrate surface such that the distance between thesliders is minimized without having the sliders contact each other. As aresult, gaps or recesses are formed between the rows and columns. Thedistance between the rows and columns may range from about 50 to about1000 micrometers and can be as small as about 100 micrometers or less.The depth of the gaps depends upon the thicknesses of the sliders andmay range from about 100 to about 300 micrometers. While the encapsulantfluid may be dispensed in any manner effective to bond the sliderswithout contacting the coplanar slider surfaces, encapsulant fluidshould flow in certain ways to form certain embodiments of the sliderassembly. For example, in order to form void-free slider assemblies,encapsulant fluid is preferably injected or drawn into the gaps orrecesses between the rows and the columns. In addition, to form sliderassemblies having a contiguous planar surface comprised of at least oneencapsulant region and containing the coplanar slider surfaces, theencapsulant fluid preferably conforms to the slider surfaces and theplanar substrate surface to which the fluid comes into contact.Furthermore by bringing the level of encapsulant fluid to the same orhigher level as the sliders, an additional planar surface opposing thecoplanar sliders surfaces may be formed. Molds and equivalents thereofmay be advantageously used to confine encapsulant fluid flow.

The ability of the encapsulant fluid to gap-fill is dependent on anumber of factors. One particularly important factor is the viscosity ofthe encapsulant fluid. Viscosity is a measure of resistance of a fluidto sheer forces and is often roughly inversely proportional to thegap-filling ability of the fluid. Typically, the encapsulant fluid has alow initial viscosity, e.g., less than about 1000 centistokes.Preferably, the initial viscosity is no more than about 800 centistokes.More preferably, the initial viscosity is no more than about 500centistokes. For certain encapsulant fluids, an initial viscosity ofabout 20 to about 200 centistokes represents an optimal range forgap-filling ability. For encapsulant fluids that contain a solvent, ahigher solvent content tends to correlate with lower viscosity. In someinstances, an encapsulant fluid containing a polymer dissolved in asolvent exhibits a preferred viscosity at a solvent content of 30 wt %to about 50 wt %. An optimal viscosity may sometimes be found when thesolvent is present in a range of about 40 wt % to about 45 wt % of theencapsulation fluid.

Surface forces may also play a role in determining the ability of theencapsulant fluid to gap-fill. In general, the ability of an encapsulantfluid to fill a gap will depend, in part, on the affinity of the surfaceof the gap to the encapsulant fluid. Thus, proper selection of theencapsulant fluid according to the surface properties of the substrateand/or the sliders may enhance gap filling via capillary action.

Once proper distribution of the encapsulant fluid is achieved, thedispensed encapsulant fluid is subjected to conditions effective for thefluid to form a debondable solid encapsulant from the encapsulant fluid.Depending on the encapsulant used, solidification may take place via anumber of different mechanisms. For example, in situ crosslinking and/orpolymerization may be effected in the encapsulant fluid. In someinstances, such reactions may be photoinitiated. In addition, when theencapsulation fluid contains a polymer dissolved in a solvent, formationof a solid encapsulant may involve removing the solvent. This may beachieved by subjecting the encapsulation fluid to heat or reducedpressure.

In some instances, a combination of mechanisms may be employed. Forexample, a slider assembly may be formed in the manner as discussedabove wherein the encapsulation fluid is comprised of a first polymer, asolvent, and a composition that is polymerizable and/or crosslinkable.Once dispensed, the solvent is evaporated to form a debondable solidencapsulant comprising the first polymer and a second polymer preparedvia polymerization and/or crosslinking of the composition from theencapsulation fluid.

An example of the above-described method for forming the assembly isillustrated in FIG. 2. FIGS. 2A and 2B depict the placement of sliders10 in a four-by-four rectilinear array on a tape 12 having asubstantially planar upper surface 14. The upper surface 14 of the tapehas a coating of a pressure-sensitive adhesive 16 coated on an uppersurface thereof. Each slider has an air-bearing surface 18 and anopposing back surface 20. The air-bearing surfaces 18 are placed facingdownward to face the upper surface 14 of the tape and to contact thepressure sensitive adhesive 16.

Also provided is a rectangular frame 21 in contact with the pressuresensitive adhesive 16. Together with the frame 21, the tape 12 serves asa mold or container to confine the encapsulant fluid dispensed thereon.

FIGS. 2C and 2D depict the formation of an encapsulated array. Ingeneral, FIGS. 2C and 2D are identical to FIGS. 2A and 2B, except thatan encapsulant fluid 22 is dispensed on the tape 12 within the frame 21to a level that coincides with the exposed surface 20 of the sliders 10.As depicted in FIG. 2D, the encapsulant fluid conforms to the sides ofthe sliders 10 as well as the profile of the upper surface 14 of thetape. In addition, no wicking of the encapsulant fluid 22 is shownbetween air-bearing surfaces 18 of the sliders 10 and the adhesive 16.

As depicted in FIGS. 2E and 2F, once the encapsulant fluid 22 solidifiesto form the encapsulant 22S, the tape 12 may be removed to form theslider assembly 24. The slider assembly 24 has two opposing parallelplanar surfaces indicated at 26 and 28. Surface 26 is formed in part byair-bearing surfaces 18 of the sliders 10, while surface 28 is formed inpart by the back surfaces 20 of the sliders 10. A carrier 30 is attachedto surface 28.

Method for Patterning an Air-Bearing Surface of a Slider

The invention further provides a method for patterning an air-bearingsurface of a slider. The method involves applying a resist layer on anair-bearing surface of a slider, wherein at least a portion of theslider other than the air-bearing surface is encapsulated in adebondable solid encapsulant comprising styrene and acrylate polymers. Aportion of the resist layer is removed to uncover a portion of theair-bearing surface in a patternwise manner. In some instances, materialis added to the uncovered portion of the air-bearing surface. Inaddition or in the alternative, material may be removed from theuncovered portion of the air-bearing surface. As a result, theair-bearing surface is patterned. Notably, the encapsulant ismechanically stable upon exposure to any fluid employed to apply theresist layer, to remove the resist layer, to add material to theair-bearing surface and/or to remove material from the air-bearingsurface.

In general, the resist layer may be applied using any of a number ofconventional techniques, e.g., sequential spin coating, casting,extruding or the like. For example, a resist composition may be providedin a liquid solvent on the substrate surface, and heated to remove thesolvent. As a result, the resist layer typically has a thickness ofabout 1 to about 20 micrometers, optionally about 2 to about 10micrometers. To effect controlled removal of portions of the resistlayer, it is preferred that the resist layer be applied with a uniformthickness.

To facilitate the patternwise removal of a portion of the resist layer,the resist layer may be comprised of a photosensitive composition thathas been exposed to photons in the patternwise manner. Photosensitivecompositions are typically polymeric and exhibit different removalproperties after exposure to electromagnetic radiation. For example,photosensitive compositions may exhibit increased mechanical integrityresulting from radiation-initiated crosslinking or decreased mechanicalintegrity resulting from radiation-initiated breakdown. Examples ofphotosensitive compositions include, but are not limited to, positiveand negative resists that are responsive to photon or electron beams.Positive photoresist compositions are more easily removed after exposureto radiation. Positive photoresists may include polymeric materials withweak links that degrade by the process of scission or contain aphotoactive component that renders the composition more soluble to asolvent upon irradiation. Negative photoresist compositions, on theother hand, become more difficult to remove after exposure to radiation.

Suitable photosensitive compositions such as photoresists may comprise,for example, poly(methyl methacrylate) (“PMMA”) or copolymers thereofsuch as poly(methyl methacrylate-co-t-butylmethacrylate), apoly(lactide) such as poly(lactide-co-glycolide), polymethacrylamide,polyoxymethylene, polyalkenesulfone, orpoly(glycidylmethacrylate-co-ethyl acrylate), epoxies, phenolics,polymers thereof, copolymers thereof, and combinations thereof.Photosensitive compositions may also contains photoactive compoundsincluding, but not limited to, diazonaphthoquinones, iodonium andsulfonium salts and o-nitrobenzyl esters.

Typically, the resist is irradiated using photonic radiation, e.g.,ultraviolet radiation and a mask to provide the desired pattern.Following exposure, the resist layer may be developed using a suitablesolvent to remove the irradiated or the non-irradiated areas to uncovera portion of each slider surface. One of ordinary skill in the art willrecognize that there are many commercially available photoresists havingdifferent exposure wavelengths, and that custom photoresist compositionsmay be formulated to have a particular exposure wavelength.

When one wishes to add material to the uncovered portion of theair-bearing surface, various techniques are known in the art ofsemiconductor fabrication. Exemplary techniques include, but are notlimited to, evaporation, sputtering, chemical vapor position, andelectroplating. Notably, deposition techniques must be chosen accordingto the material. For example, metals may be deposited by evaporation,sputtering, electroplating, chemical vapor deposition, etc.

In order to effect a high degree of control over the addition ofmaterial to the air-bearing surface, vacuum deposition technology isgenerally preferred. Such vacuum processes include, but are not limitedto, cathodic arc physical vapor deposition, electron-beam evaporation,enhanced arc physical vapor deposition, chemical vapor deposition,magnetronic sputtering, molecular beam epitaxy, combinations of suchtechniques and a variety of other techniques known to one of ordinaryskill in the art.

When one wishes to remove material from the air-bearing surface, anetchant may be used to effect chemical, mechanical and/or physicalremoval material. In some instances, an isotropic etchant may be used toremove material in a direction-invariant manner such that no differenceis exhibited in directional etching rate. Alternatively, an anisotropicetchant may be used to remove material preferentially in a particulardirection, e.g., according to crystallographic orientation of the solidbody or the direction of the light energy particles for light assistedetching. In some instances, an ionized gas such as argon-based orfluorine-based plasma or an ion beam may be used as an enchant. A liquidetchant may also be advantageously used as well.

Further information regarding patterning and etching processes usinglithographic techniques is provided in Sze (1983), “Lithography,” VSLITechnology, McGraw-Hill Book Company.

FIG. 3 depicts an example of the above-described method for patterningan air-bearing surface of a plurality of sliders provided in the form ofthe slider assembly depicted in FIG. 2. As shown in FIG. 3A, the sliderassembly 24 is placed on a flat surface such that the air-bearingsurface 28 of the assembly faces upward and the carrier 30 contacts theflat surface. A photoresist layer 32 is applied in a uniform thicknessover the air-bearing surface. Due to the planarization of air-bearingsurface 28, the resist layer may be applied as a thin, high-resolutioncoating. Planarized surfaces have been coated with resist layers havinga preferred thickness of about 1 to 25 micrometers and a more preferredthickness of about 2.0 to 15 micrometers. This provides a resolution ofabout 200 micrometers to 5 micrometers.

FIG. 3B depicts the patternwise exposure of the photoresist layer 32 tophotons. This is performed by providing a mask 34 having transparentregions 36 and opaque regions 38. A source 40 of photons is provided inorder to generate radiation, preferably substantially collimated, havinga wavelength to which the photoresist layer 32 is responsive. Typically,the wavelength is an ultraviolet wavelength. The mask 34 is placedbetween the photon source 40 and the photoresist layer 32 such that thetransparent regions 36 are in alignment with the air-bearing surfaces 18of the sliders 10. As a result, radiation is transmitted through thetransparent regions 36 of the mask 34, and the photoresist layer isconverted into a patterned layer comprising the exposed and theunexposed regions. In some instances, grayscale masks are employed.

FIG. 3C depicts the removal of a resist layer according to the patternformed in FIG. 3B. This is achieved by developing the exposed portionsof the photoresist layer 32 to facilitate removal thereof. In this case,the exposed portions are washed away with a solvent, leaving theunexposed portions intact. As a result, portions of the air-bearingsurfaces 18 are uncovered.

FIG. 3D depicts the removal of material from the uncovered slidersurfaces 18 by exposing the surfaces 18 to an etchant. By debonding theencapsulant 22S from the sliders, as depicted in FIG. 3E, encapsulantfree sliders 10, having patterned air-bearing surfaces 18, are formed.As discussed above, debonding may involve using a solvent to wash awaythe encapsulant or applying heat to liquefy, vaporize and/or discomposethe encapsulant. Mechanical action may also be used sparingly to assistin the debonding process. For example, soft brushes may be used inconjunction with a solvent to remove encapsulant from the sliders sothat no residue is left behind.

Encapsulant Fluids and Debondable Encapsulants

The selection of encapsulant fluids and debondable encapsulantsrepresents a particularly important aspect of the invention. Asdiscussed above, the encapsulant fluids are selected for their abilityto gap-fill and to form slider arrays having high planarization values.However, encapsulant fluids having a desirable gap-filling capabilitytend to form encapsulants having poor debonding performance. Thus, whilea number of encapsulant materials have been investigated, only arelative few have been found to exhibit both excellent gap-fillingcapabilities and bonding/debonding performance.

Styrene polymer blends represent a class of encapsulant material foundsuitable for use with the present invention. In particular, it has beendemonstrated that a blend of low molecular weight polystyrene copolymersand polyacrylate can be used to form a readily debondable encapsulant.In encapsulant fluid form, such polymeric blends exhibit excellentgap-filling performance and planarization ability as well as exceptionaldebondability. The facile debonding is attributed to the observationthat the blend is primarily thermoplastic rather than thermosetting.

A variety of low molecular weight hydrogenated styrene copolymersavailable from either ExxonMobile Chemical Company (Houston, Tex.) orArakawa Forest Chemical Industries, Ltd. Corporation (Osaka, Japan) havebeen studied. These materials are amorphous, soluble in nonpolarsolvents and are available with softening points ranging from 70–150°C., preferably at least 130° C. The viscosities at the softening pointsmade solventless filling of the arrays difficult. In addition, the pureresins tended to fracture upon cooling at a thickness of severalmicrometers. To overcome such a drawback, it has been found thatblending acrylates with the hydrocarbon resins produces a significantlytougher material that is not prone to cracking.

An exemplary encapsulant fluid formulation contained hydrogenatedpolystyrene resin, isobornyl acrylate monomer, polyfunctional acrylatecrosslinker and a photopackage. The hydrogenated polystyrene was readilydissolved (25–40%) in isobornyl acrylate to provide an encapsulantsolution in the desired viscosity range (200–800 centistokes). Theformulation also contained trimethylolpropane triacrylate (3–5%) and aphotoinitiator (3%). The photoinitiator was available under thetrademark of Irgacure® 651, registered to Ciba-Geigy Corporation(Tarrytown, N.Y.). No additional solvent was included in theformulation.

The encapsulant fluid was applied in a single filling operation for arectilinear array type slider assembly and cured using a mercury lightsource for 4–8 minutes. The encapsulated sliders were subjected to astandard photolithographic patterning process that uses propylene glycolmethyl ether acetate. After carrier attachment, the step height for thismaterial was measured at less than 6 micrometers. The best solventresistance was exhibited by the higher melting hydrogenated polystyreneresins. Such resins are available under the Trademark Arkon® 140. It wasfound that presence of trimethylolpropane triacrylate in the formulationimproved the encapsulant's resistance to thermal deformation. Aftercompletion of the patterning process, the sliders were cleanly debondedusing mesitylene at 50° C. with sonication.

It should be noted that the bonding and debonding performance of anencapsulant is dependent on a variety of factors and is not generallypredicable solely based on the chemical structure of the encapsulant.Thus, for example, while certain members of a class of polymers mayexhibit acceptable bonding and debonding performance, other members ofthe same class are not. Thus, when a class of polymers is generallyidentified as exhibiting acceptable bonding/debonding performance,specific polymers within that class which suffer from poor bondingand/or debonding performance is specifically excluded by the invention.For example, while the polymer discussed above have generally found toexhibit acceptable bonding/debonding performance, it is expected thatnot all such polymers can be used to form a debondable encapsulant.According, employment of such unsuitable polymers in an encapsulant isnot encompassed by the invention.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, theforegoing description is intended to illustrate and not limit the scopeof the invention. Other aspects, advantages and modifications will beapparent to those skilled in the art to which the invention pertains.All patents and publications cited herein are incorporated by referencein their entireties.

1. A slider assembly comprising a plurality of sliders arranged in anarray and bonded by a debondable solidified fluidic encapsulant, whereinthe encapsulant is comprised of fluidic styrene and acrylate polymericmaterials to minimize gaps between sliders, each slider has a surfacethat is free from the encapsulant, and the encapsulant-free surfaces aresubstantially coplanar to each other.
 2. The slider assembly of claim 1,having a contiguous planar surface comprised of at least one encapsulantregion and containing the coplanar slider surfaces.
 3. The sliderassembly of claim 2, wherein the array is a rectilinear array.
 4. Theslider assembly of claim 3, wherein the sliders do not contact eachother.
 5. The slider assembly of claim 3, wherein the substantiallycoplanar surfaces of the sliders are each an air-bearing surface.
 6. Theslider assembly of claim 5, further comprising a substrate in contactwith the air-bearing surfaces.
 7. The slider assembly of claim 6,wherein the substrate is comprised of a laminate of a flexible tape andan adhesive, wherein the adhesive is in contact with the air-bearingsurfaces.
 8. The slider assembly of claim 7, wherein the adhesive is apressure sensitive adhesive.
 9. The slider assembly of claim 7, whereinthe adhesive preferentially adheres to the tape over the air-bearingsurfaces.
 10. The slider assembly of claim 5, further comprising aresist layer on the air-bearing surfaces, wherein the encapsulant ismechanically stable upon exposure to the resist layer or any componentthereof.
 11. The slider assembly of claim 10, wherein the encapsulant issubject to solvation by a solvent not found in the resist layer.
 12. Theslider assembly of claim 11, wherein the solvent is comprised of anonpolar solvent.
 13. The slider assembly of claim 3, wherein theencapsulant does not substantially outgas under vacuum.
 14. The sliderassembly of claim 3, further comprising a carrier attached to theencapsulant and/or at least one slider, wherein the carrier does notcover any of the coplanar slider surfaces.
 15. The slider assembly ofclaim 1, wherein the styrene polymeric material is a hydrogenatedstyrene copolymer.
 16. The slider assembly of claim 15, wherein thehydrogenated styrene copolymer has a softening temperature of about 70°C. to about 150° C.
 17. The slider assembly of claim 16, wherein thesoftening temperature is at least about 130° C.
 18. The slider assemblyof claim 1, wherein the acrylate polymeric material is prepared via insitu polymerization of acrylate monomers.
 19. The slider assembly ofclaim 1, wherein the acrylate polymeric material is prepared viaphotoinitiated polymerization of acrylate monomers.